This invention relates to dispersants, dispersants with improved engine performance, dispersants with viscosity index (VI) improving properties, and dispersant VI improvers from functionalized diene polymers, and methods of their use. More particularly, the invention relates to dispersants, dispersants with VI improving properties, and dispersant VI improvers from selectively hydrogenated copolymers prepared using conjugated dienes. The invention is additionally directed to dispersants, dispersants with VI improving properties, and dispersant VI improvers from chemically modified derivatives of the above polymers.
Liquid elastomers are well known and are used in various applications. For example, many functionally terminated polybutadiene liquid elastomers are known. These materials are generally highly unsaturated and frequently form the base polymer for polyurethane formulations. The preparation and application of hydroxy-terminated polybutadiene is detailed by J. C. Brosse et al. in Hydroxyl-terminated polymers obtained by free radical polymerization--Synthesis, characterization and applications, Advances in Polymer Science 81, Springer-Verlag, Berlin, Heidelberg, 1987, pp. 167-220.
Also, liquid polymers possessing acrylate, carboxy- or mercapto-terminals are known. In addition to butadiene, it is known to utilize isoprene as the base monomer for the liquid elastomers. The liquid elastomers may contain additional monomers, such as styrene or acrylonitrile, for controlling compatibility in blends with polar materials, such as epoxy resins.
Also known in the prior art are pure hydrocarbon, non-functionalized liquid rubbers. These liquid elastomers contain varying degrees of unsaturation for utilization in vulcanization. Typical of highly unsaturated liquid elastomers is polybutadiene, e.g., that sold under the name RICON by Ricon Resins, Inc. A liquid polyisoprene which has been hydrogenated to saturate 90% of its original double bonds is marketed as LIR-290 by Kuraray Isoprene Chemical Co. Ltd. Still more highly saturated are liquid butyl rubbers available from Hardman Rubber Co., and Trilene, a liquid ethylene-propylene-diene rubber (EPDM) available from Uniroyal Chemical Co. The more highly saturated liquid elastomers exhibit good oxidation and ozone resistance properties.
Falk, Journal of Polymer Science: PART A-1, 9:2617-23 (1971), the entire contents of which are incorporated herein by reference, discloses a method of hydrogenating 1,4,-polybutadiene in the presence of 1,4-polyisoprene. More particularly, Falk discloses hydrogenation of the 1,4-polybutadiene block segment in the block copolymer of 1,4-polybutadiene-1,4-polyisoprene-1,4-polybutadiene and in random copolymers of butadiene and isoprene, with both polymerized monomers having predominantly 1,4-microstructure. Hydrogenation is conducted in the presence of hydrogen and a catalyst made by the reaction of organoaluminum or lithium compounds with transition metal salts of 2-ethylhexanoic acid. Falk, Die Angewandte Chemie, 21(286):17-23 (1972), the entire contents of which are also incorporated herein by reference, discloses the hydrogenation of 1,4-polybutadiene segments in a block copolymer of 1,4-polybutadiene-1,4-polyisoprene-1,4-polybutadiene.
Hoxmeier, Published European Patent Application 88202449.0, filed on Nov. 2, 1988, Publication Number 0 315 280, published on May 10, 1989, discloses a method of selectively hydrogenating a polymer made from at least two different conjugated diolefins. One of the two diolefins is more substituted in the 2, 3 and/or 4 carbon atoms than the other diolefin and produces tri- or tetra-substituted double bond after polymerization. The selective hydrogenation is conducted under such conditions as to hydrogenate the ethylenic unsaturation incorporated into the polymer from the lesser substituted conjugated diolefin, while leaving unsaturated at least a portion of the tri- or tetra-substituted unsaturation incorporated into the polymer by the more substituted conjugated diolefin.
Mohajer et al., Hydrogenated linear block copolymers of butadiene and isoprene: Effects of variation of composition and sequence architecture on properties, Polymer 23:1523-35 (1982) discloses essentially completely hydrogenated butadiene-isoprene-butadiene (HBIB), HIBI and HBI block copolymers in which butadiene has predominantly 1,4-microstructure.
Kuraray K K, Japanese published patent application Number JP-328 729, filed on Dec. 12, 1987, published on Jul. 4, 1989, discloses a resin composition comprising 70-99% wt. of a polyolefin (preferably polyethylene or polypropylene) and 1-30% wt. of a copolymer obtained by hydrogenation of at least 50% of unsaturated bond of isoprene/butadiene copolymer.
Ashless dispersants are additives to lubricant fluids such as fuels and lubricating oils which improve the dispersability of the fluids or improve their viscometric properties. Typically, such dispersants are modified polymers, having an oleophilic polymer backbone to assure good solubility and to maintain particles suspended in the oil, and polar functionality to bind or attach to oxidation products and sludge. Dispersants generally have a solubilizing oleophilic (hydrophobic) tail and a polar (hydrophilic) head, forming micelles when actively bound to sludge.
Common dispersants include polyisobutenes which have been modified by the ene reaction to include functional groups such as succinimides, hydroxyethyl imides, succinate esters/amides, and oxazolines. Other dispersants include Mannich base derivatives of polybutenes, ethylene propylene polymers, and acrylic polymers.
Traditionally, dispersants have been polybutenes functionalized at one site in the molecule via an ene reaction with maleic anhydride followed by imidization with a polyamine. The polybutenes are typically 500-2,000 in molecular weight, and due to the polymerization process employed in their manufacture, have no more than one double bond per polybutene molecule. Accordingly, the number of potential functional groups per chain is limited to about one. Typically, this site is at a terminal portion of the molecule. Moreover, it is generally accepted that, in order to obtain beneficial dispersant properties, a molecule must have at least one functional group per approximately 2,000 molecular weight. Consequently, the molecular weight of traditional polybutene dispersants cannot exceed 2,000 if the desired functionality/hydrocarbon ratio is to be maintained. In addition, traditional dispersants have had molecular structures which have limited the placement of functional groups, generally requiring that such groups be placed at the terminal regions of the molecules.
The polymerization process for the traditional butene polymers has also generated products having an unacceptably wide distribution of molecular weights, i.e., an unacceptably high ratio of weight average molecular weight (M.sub.w) to number average molecular weight (M.sub.n). Typically, such distributions are M.sub.w /M.sub.n.gtoreq.2.5, producing compositions whose dispersant properties are not well defined.
Moreover, functionalization reactions in these polymers have typically yielded substantial quantities of undesirable by-products such as insoluble modified polymers of variant molecular weight. Functionalization reactions can also result in compounds which contain undesirable chemical moieties such as chlorine.
U.S. Pat. No. 4,007,121 to Holder et al. describes lubricant additives which include polymers such as ethylene propylene polymers (EPT) having N-hydrocarbylcarboxamide groups.
U.S. Pat. Nos. 3,868,330 and 4,234,435 to Meinhardt et al. disclose carboxylic acid acylating agents for modification of lubricant additives. Modified polyalkenes are described such as polyisobutene-substituted succinic acylating agents having M.sub.n of 1300-5000 and M.sub.w /M.sub.n of 1.5-4. These processes employ chlorination to provide greater functionality.
Heretofore, the art has failed to produce dispersants and dispersant VI improvers having selective and controllable amounts of polar functionality in their polymeric structure. Thus, the art has failed to provide any means of developing dispersants and dispersant VI improvers having higher molecular weights and/or higher amounts of functionalization per molecule. The art has also failed to provide dispersant polymers having desirably narrow molecular weight distributions to avoid the presence of by-products which degrade dispersant performance. The art has also failed to provide dispersant and VI improving compositions which exhibit good thermal stability.
Accordingly, it is a purpose of this invention to provide dispersants and dispersant VI improvers having polymeric structures which permit highly selective control of the degree of unsaturation and consequent functionalization. Unique materials can also be obtained by chemical modification of the polymers of this invention since the polymers can be selectively modified at controllable sites, such as at random sites or at the terminal ends of the molecules.
It is an additional purpose of this invention to provide a method for the production of dispersants and dispersant VI improvers from polymers having controlled amounts of unsaturation incorporated randomly in an otherwise saturated backbone. In contrast to EPDM-based dispersants, the level of unsaturation can be inexpensively and easily controlled, e.g., from 1% to 50%, to provide a wide variation in functionalizability.
It is a further purpose of the invention to provide dispersant and VI improving polymers having narrow molecular weight distributions and a concomitant lack of undesirable by-products, thereby providing more precisely tailored dispersant and/or VI improving properties.
It is still a further purpose of this invention to provide dispersants having improved engine performance.